Among the bikes in my stable is a department store tandem that really isn't worth much, but would be enjoyable to ride with my wife. Like many department store bikes this one was not assembled correctly and now the pedal threads on the right front crank are beyond stripped, there are millimeters of smooth clearance around where it would screw in. It doesn't appear that it could be re-threaded.

The problem is, on a normal bike the right crank has the splines for the chainrings, and the left is unadorned. On the front crank of a tandem this is backwards. So while I can find replacement left crank arms, what I really need is a plain 170 mm right crank arm.

The cheap options are fitting a helicoil or equivalent to replace the thread, or finding another cheap tandem that's been wrecked and get the part from that. The helicoil is probably the easiest option, but if you can find a wrecked tandem that will possibly be cheaper.

There are companies that re-tap cranks for tandems (Greenspeed is one) but that adds $50 or so to the cost, however it may be less because they have a surplus of spider-less cranks (a tandem needs three spiders and one spiderless crank, leaving two spare). It would be worth asking them.

There is a nice bargain priced set on ebay right now - Sugino, search 'tandem crank' should get you there. Get your bid in, sure the crank will be good and you will have spares for all the rest. Failing that you can get a spare from Middleburn in the UK - pop them an email.